Applicator syringe for a dental compound

ABSTRACT

Applicator syringe for a dental compound, with a syringe body (1) tapering into a thin discharge tube (3) and with a piston (5) displaceable in it, the applicator syringe being intended for once-only use. To avoid the need for special actuating tools, but make easy use possible, the effective cross-sectional surface is very small, in particular with a ratio of the useful stroke to the diameter of the syringe piston of at least approximately 10. So that the syringe can nevertheless be filled easily, the diameter of the cylindrical space in the rear portion of the latter is larger than the piston diameter. The syringe body (1) is first produced in a straight form and only thereafter is the discharge tube (3) bent.

This is a divisional of co-pending application Ser. No. 060,245 filed onMay 29, 1987, now U.S. Pat. No. 4,798,596.

The invention relates to a disposable applicator syringe for a dentalcompound, with a syringe body enclosing a cylindrical space and taperinginto a thin discharge tube, and with a piston displaceable in thecylindrical space, in the state of rest the cylindrical space receivingthe dental compound in a front portion and the piston in a rear portion.

It is customary for the dentist to pick up the separately mixed dentalcompound by means of a re-usable syringe which ends in a thin dischargetube and which contains a displaceable piston, in order to apply it bymeans of this syringe (GB-A-734,983 and US-A No. 4,184,490). Thisoperation is complicated, especially since the syringe has to be cleanedand sterilized after each use.

Applicator syringes intended for once-only use and containing mercuryand silver filings in separate chambers have therefore been developed,these components being mixed in the syringe itself (GermanOffenlegungsschrift No. 2,903,331); but these syringes have provedinappropriate, because there are difficulties in storing the mercury inthem in a sealed manner and combining the components in exact quantitiesand mixing them completely.

The principle of the so-called disposable syringes was first adoptedsuccessfully in connection with photo-setting single-component fillingcompounds contained in syringe-like applicator cartridges. Thesecomprise a syringe body with a cylinder displaceable in it, and a curveddischarge tube. Since the force exerted to displace the piston in thesyringe body is considerable, to use it a tool, for example of tong-likeor pistol-like design, is required (German Auslegeschrift No. 2,045,509,German Offenlegungsschrift No. 2,110,463, German Offenlegungsschrift No.3,235,232 and U.S. Pat. No. 4,391,590). The need for a special tool is adisadvantage, especially since it could come into contact with thepatient's mouth and would therefore have to be sterilized. Theproduction of these disposable syringes involves a high outlay, becausethe curved shape of the discharge tubes for forming the cavity require amulti-part core of complicated construction. Another disadvantage ofthis type of production is that the curved discharge tube can only berelatively short.

Applicator syringes for single-component filling compounds, which have alarge holding capacity and which are intended for repeated use, are alsoknown (German Offenlegungsschrift No. 3,212,187). These too should besterilized before each use, but this is scarcely possible because theyare in a filled state.

The object on which the invention is based is, therefore, to provide aninexpensive disposable applicator syringe which can be employed withouta tool, but which nevertheless ensures hygienic use. Furthermore, theobject on which the invention is based is to provide a simple processfor producing such an applicator syringe with a curved discharge tubewhich can be of any length.

In the solution according to the invention, the syringe body and thepiston designed as a rod are made thin, in particular with a ratio ofthe effective stroke to the diameter of the cylindrical space and thesyringe piston of at least approximately 10, and the diameter of thepiston is less than the diameter in the rear portion of the cylindricalspace.

The invention, to provide an applicator syringe designed as a whole foronce-only use, had to overcome two difficulties. One is that the forcerequired to propel the piston must be so low that there is no need for aspecial tool. The other is that, because of the need for competitivenessin the field of small and simple applicator capsules, the outlay interms of production must be kept very low, so that it is possible tocompete with the applicator capsules mentioned above.

Because of the choice of an unusually small piston diameter which isappropriately no greater than approximately 10 or preferably 7 mm², theforce required to expel the compound from a nozzle orifice ofpredetermined size is reduced considerably. Although the small pistondiameter results in a considerable increase in the necessary stroke fora predetermined discharge volume of, for example, 100 mm³, nevertheless,in contrast to a tool, a stroke of the order of, for example, 3 cmpresents no problem for the human hand. As regards the outlay involvedin the applicator syringe according to the invention, this depends, onthe one hand, on the quality of the piston packing. In comparison withthe known applicator capsules, to meet the same sealing requirements thecross-sectional tolerances in the syringe according to the invention canbe substantially greater than in the known capsules because of theshorter peripheral length of the sealing zone. On the other hand, theproduction outlay depends on how complicated is the filling operationwhich, in the syringe according to the invention, is very simple.

Because the piston does not rest directly against the cylindrical wallin the rear portion of the cylindrical space in which it is located whenthe applicator syringe is in the state of rest ready for use, the pistoncan be pushed into the cylindrical space even after the compound hasbeen introduced into the front portion of the cylindrical space, sincethe gas (air or inert gas) located between the compound and the pistoncan escape through the gap between the cylinder wall and the piston. Ifthe piston has a sealing lip formed on it, the diameter of the latter isto be taken as the decisive piston diameter which should be somewhatless than the diameter of the cylindrical space in that rear part of thesyringe body which is not filled with the compound and in which thepiston will be located. As soon as the piston strikes the compound or ispressed against it, the pressure exerted on the sealing lip of thepiston increases and presses a sealing lip against the cylinder wall,even if the relaxed diameter of the sealing lip when it strikes thecompound is still somewhat less than that of the cylindrical space. Forthese and other reasons, it is not necessary for the piston diameter tobe equal to the diameter of the cylindrical space exactly at theboundary between the front portion filled with the compound and the rearportion in which the piston is to be located.

Since the cylindrical space of the syringe body is long and thin, toproduce the syringes according to the invention it is not possible touse the known production process, in which the syringe body and thecurved discharge tube are produced in a single injection-mouldingoperation, since the long thin cylindrical space prevents the use ofmulti-part curved moulding cores. However, the long thin shape of thesyringe according to the invention makes it possible to adopt asubstantially simpler production process, in which the syringe body andthe discharge tube are first produced axially in alignment with oneanother by the use of a single injection mould with only one uniformcore and only thereafter is the discharge tube bent when thethermoplastic material is in the still hot or reheated state. Thisprocess cannot be used for the known applicator capsules, because inthese the discharge tube is too thick in relation to its length. Thus,the syringe according to the invention is simple to produce because ofits thin shape with a low ratio of the clear cross-sectional surface ofthe cylindrical space to that of the end of the discharge tube, thisratio advantageously being no greater than 5:1 and preferably 3:1.

The invention is explained in detail below with reference to the drawingwhich illustrates an advantageous examplary embodiment. In the drawing:

FIG. 1 shows a longitudinal section through an applicator syringeaccording to the invention,

FIG. 2 shows the syringe body after the first production step, and

FIG. 3 shows a representation with a greatly enlarged diameter.

The applicator syringe consists of the syringe body (1) which encloses acylindrical space (2) for receiving the viscous compound and at the endtapers integrally into the thin discharge tube (3) and which has agripping flange (4), and of the rod-like piston (5) with the grippingplate (6). The piston (5) consists of a material resistant to bending,so that, despite its thinness, it does not bend under the propulsiveforces. Suitable materials are polypropylene, polyethylene or polyamide,of sufficient elasticity for the syringe body and glass-fibre-reinforcedplastic for the piston.

The discharge tube (3) can be equipped with a removable closing cap. Toprotect the compound to be stored in the syringe against harmfulinfluences, it is also possible, instead, for the appliance to be weldedinto a film bag or packaged safely in another way.

The cross-sectional size of the piston (5) and of the cylindrical space(2) is appropriately between 1 and 7 mm².

The useful stroke of the piston (5) is the distance (7) over which itcan be displaced between its position of rest ready for use and itscompletely pushed-in position.

In a syringe according to the invention which has proved appropriate inpractice, the piston cross-section is 6 mm² and the useful stroke isapproximately 25 mm.

The syringe body is produced, for example, by injection moulding in theshape shown in FIG. 2. The production mould can be simple, because onlya single straight mould core is necessary for forming the interior ofthe syringe body including the interior of the discharge tube. Onlythereafter is the discharge tube bent, and this presents no problembecause the discharge tube is relatively thin even in its part adjacentto the cylindrical part of the syringe body, and its diameter does notchange greatly over its length.

A suitable seal should be provided between the piston (5) and the wall(8) surrounding it. To ensure this, as is known, the piston can have aslight oversize exceeding the clear diameter of the cylindrical space(9) and the cylinder wall can be appropriately elastic, so that, ininteraction with the piston periphery, it expands elastically and restsagainst the piston free of gaps. For this purpose, the piston can bethickened at its front end or have a sealing lip.

The preferred embodiment is described below with reference to FIG. 3which shows the arrangement according to FIG. 1 over-enlarged in termsof diameter. According to this, the cylinder wall (8) is not exactlycylindrical, but slightly conical, so that it widens a little towardsthe end located on the same side as the piston. The piston (5), at itsfront end, carries an encircling sealing lip (10), the diameter of whichis a little less than the clear diameter of the cylindrical space (9) inthe rear portion (11) of the syringe body which remains empty, that isto say filled with gas, after the compound (13) has been introduced inthe region (12). When the piston (5) is pushed into the syringe bodyafter the compound has been introduced, the gas located between them cantherefore be expelled through the gap between the wall (8) and thesealing lip (10), until the piston end rests against the compound (13),as indicated at (14) in FIG. 3, or has at least come very close to it.The dimensions of the piston and cylindrical space are such that, inthis position, the sealing lip (10) approximately reaches the cylinderwall (8). But it does not matter if, even at this point, the diameter ofthe lip (10) is still somewhat less than that of the wall (8), becausewhen the compound is reached the pressure prevailing in front of thepiston increases to such an extent that the lip (10) is pressed outwardsagainst the cylinder wall.

I claim:
 1. A disposable applicator syringe for a dental compound,comprising:a tubular member made from an elastically yielding polymericmaterial having a rear entrance end portion, a smoothly curved frontdischarge end portion, an intermediate portion between the end portions,and a continuous, substantially cylindrical central channel extendingfrom the entrance end portion to the discharge end portion through theintermediate portion, the channel at least in the intermediate portionhaving a smaller diameter than the channel in the entrance end portionand a clear cross sectional area no greater than about 10 mm², theintermediate portion being adapted for receiving a predeterminedquantity of viscous dental compound to be discharged through saiddischarge end portion, wherein the cross sectional area of the channelthrough the intermediate portion and discharge end portion reduces withsubstantially smooth continuity by no greater than a ratio of aboutthree; and a piston in the form of an elongated rod having a headportion including annular lip means defining the diameter of the head,which is less than the channel diameter in the entrance end portion, thepiston adapted to be manually advanced through the entrance end portionand the intermediate portion into contact with the dental compound suchthat the lip means are pressed radially outwardly by the compound intosealing engagement with the wall of the channel, the head of the pistonhaving a useful stroke in the intermediate portion while advancing thecompound through the channel, said useful stroke being equal to at leastabout ten times the diameter of the channel in the intermediate portion.2. Applicator syringe according to claim 1, characterized in that thediameter of the channel through the entire intermediate portion is lessthan the diameter of the piston head.
 3. The applicator syringeaccording to claim 1, characterized in that the tubular member and thepiston are each equipped with gripping parts and the effectivecross-sectional surface of the piston head is no greater thanapproximately 10 mm².
 4. The applicator syringe according to claim 1,characterized in that the effective cross-sectional surface of thepiston head is less than approximately 7 mm².
 5. The applicator syringeaccording to claim 1, characterized in that the cross-sectional area ofthe channel through the intermediate portion and the discharge endportion reduces by a ratio no greater than approximately 5:2.